Coated fabrics



June 27, 96? F` E. WILEY 3,328,226

COATED FABR I CS Original Filed Dec. 30, 1955 5 Sheets-Sheet l o 2 4 a a /o /2 /4 /6 /a zo INVENTOR.

Pf@ 5A/ AOA/647mm FRED E. WILEY BY fwqwm ATTORN EYB F. E. WILEY COATED FABRICS June 27, i957 3 Sheets-Sheet Original Filed Dec, 30, 1955 .mAUm

June 27, 1967 Original Filed Dec.

FIG- 4.

F. E. WILEY COATED FABRICS 3 Sheets-Sheet 3 1M 'EN TOR. F FRE D E WI I EY BY @ZW 477% ATTORNEYS United States Patent O s claims. (ci. isi-92) The present application is a divisional application of copending application, Ser. No. 556,675, tiled Dec. 30, 1955, now abandoned.

This invention relates to an improved fabric.

lt is an object of the invention to provide a lightweight, high strength, low elongation, air impervious, weather resistant, coated fabric suitable for air inated radomes, used to house automatic radio and similar equipment, and for similar purposes, and which has a high bond strength of coating to fabric and which can be fabricated by means of cemented lap joints.

Another object of the invention resides in the manner of weaving, sizing and coating the fabric to secure the desired inflatable properties and utilize and preserve and take advantage of the high tenacity, strength and stability characteristic of the yarn.

Other and further objects and advantages will be made apparent from the disclosures of the following specification and claims.

ln the accompanying drawing:

FIGS. 1, 2 and 3 show in graph form the stress-strain characteristics of yarns of the present invention compared with those of the corresponding conventional high tenacity polyethylene terephthalate yarn; and

FIG. 4 shows in graph form the heat stability characteristics of yarns embodying the invention.

For radome and similar use the fabric should be light in weight, have high strength, low elongation, be impervious to air, and weather resistant, including stability under relatively high temperatures. To meet all these requirements a coated fabric is employed, and speaking generally the strength characteristics are imparted by the yarn from which the fabric is Woven while the coating imparts the air impervious and weather resistant properties. The extent to which each element of the coated fabric can contribute the maximum degree of the properties for which it is used depends in substantial measure on its ability to combine or be combined with the other in a compatible relationship that will maintain its own functional eiliciency without impairing that of the other. Ability of the coating to adhere or be made to adhere to the yarn of the fabric is an essential factor in the satisfactory performance of the fabric, as well as a capacity for construction into fabricated forms, such as radomes and other structures, by means of cemented lap joints.

The yarn-fabric-coating combination of the present invention makes possible the fabrication of radomes, for example, of less than half the weight of prior constructions with no sacrifice in strength. Taking as the unit of strength the breaking load in pounds for a one inch wide 3,328,225 Patented June 27, 1967 ice strip of the fabric divided by the weight in ounces of a square yard of the fabric, the fabric of the present invention, when coated, has a unit strength substantially greater than those heretofore available for the purpose.

In general the foregoing advantages are achieved by employing a yarn formed from the condensation product of dimethyl terephthalate and ethylene glycol (polyethylene terephthalate), pretreated, as later described, to give a strength-weight ratio 50% greater than yarns of this material heretofore commercially available, a tenacity of before and after heat shrinkage, of approximately 8.3 grams per denier and an ultimate elongation of approximately 7% before and after heat shrinkage, weaving such yarn into a fabric under predetermined conditions of twist, pretreating the fabric and curing thereon a coating of a chlorosulfonated polyethylene.

Polyethylene terephthalate yarns are commercially available, the various yarns sold by E. I. du Pont de Nemours & Company under its trademark Dacron being examples. Filaments of this material as it is initially produced have a low tenacity and high elongation and, as is done with other synthetic fibres, such as rayon, the tenacity of polyethylene terephthalate yarns have been increased by hot or cold stretching, or both. Such stretching reduces the denier of the yarn. These synthetic yarns have a marked tendency to recover after stretching and in an effort to render the stretching more permanent it has been customary to heat set the stretched yarn, that is hold it in its stretched condition at or above the stretching temperature for a short period, less than a minute.

The effects of heat setting while rendering the yarn adequately stable at ordinary use temperature does not prevent shrinkage at more elevated temperatures, and this shrinkage is accompanied by a reduction in the tenacity acquired from the stretching, and an increase in denier. Further, over the conventional stretching ranges an increase in the heat setting time, that is the period at which the yarn is held at in its stretched condition at or above the hot stretching temperature further tends to reduce the tenacity. At present the highest tenacity polyethylene terephthalate yarn commercially available (Dacron 5100) has a shrinkage of approximately 11.47 percent when subjected to a temperature, for example, of 250 F. for a period of one hour, and a tenacity after shrinkage of approximately 6 grams per denier with an elongation at break of substantially 20%. These considerations have prevented the use of these yarns for purposes such as radome fabrics Where heat cured coatings, lightweight, high tenacity and low elongation are essential requirements.

While previous practice has indicated the necessity of heat setting polyethylene terephthalate yarn to make it stable it has been found that, contrary to expectations, heat setting has less effect on the yarn as the amount of stretching is increased. It has been found, when a high tenacity polyethylene terephthalate yarn, such as Dacron 5100 is hot stretched 15%, Within a hot stretching range of substantially 325 F. to just below the melting point of the resin, that at and beyond a 15% stretch heat setting no longer effects a decrease in the 250 F. shrinkage. This important finding makes possible the elimination of the deleterious effect of the heat setting operations, and as a result inherently stable polyethylene terephthalate yarn has been obtained with tenacities of approximately 9 grams per denier and an ultimate elongation of approximately 7%, before shrinkage at 25 0 F., and tenacities approximating 8.3 grams per denier and an ultimate elongation of approximately 11% or less after such shrinkage. Another important finding is that shrinkage is not increased by greater amounts of hot stretching. Thus the 15% hot stretching while reducing the denier and substantially increasing the tenacity has not materially increased the shrinkage over that resulting from a hot stretching of the material. A factor contributing to the improved physical characteristics, particularly the improved heat stability, is believed to be a substantially vpermanent change in the crystalline strueture of the material it appearing that once the filament is stretched to a point of ultimate orientation the corresponding crystallization locks this orientation in place.

The stretch percentages given above are those additionally imposed on samples of a relatively freshly manufactured commercial high tenacity polyethylene terephthalate yarn (Dacron 5100).

The stretch under the conditions above mentioned appears to be the minimum at which this phenomena occurs, taking into consideration the variables in yarn manufacture, the hot stretch of a yarn such as Daeron 5100 preferably is carried to and for yarns of initially lower tenacity such as Daeron 5500 the percentage of stretch should, as later pointed out, -be further increased. In any event for any given yarn the stretch, whether at or above the 15% should be that which effects a substantial ultimate molecular orientation simultaneously with substantially the ultimate crystallization. For many fabric requirements (clothing, upholstery, hangings, and the like) tenacities higher and elongations lower than afforded by such yarns as are representated by Daeron 5100 and Daeron 5500 are not required, and while the hot stretching procedures of the present invention are adaptable to incorporation directly in the yarn manufacturing procedure, yarn for the purposes of the fabric of the present invention, where as later pointed out, coating curing temperatures of the order of 250 F. are employed, may be advantageously prepared from freshly manufactured high tenacity yarn presently commercially available.

A comparison of such commercial yarn (Zero Twist 50 Filament Daeron 5100) with the same yarn processed in accordance with, and producing the yarn of, the present invention is shown in FIG. l.

Referring to FIG. 1 of the drawing curve A represents the Stress-Strain curve of a sample of freshly produced Zero Twist 50 Filament Daeron 5100 yarn (160 denier) as freshly received from the manufacturer. Curve B represents the Stress-Strain curve of a sample of the same yarn after it had tbeen subjected to heat shrinkage at 248 F. for a period of one hour at no load.

Curve A shows a tenacity of approximately 6.6 grams per denier and a percentage elongation at the break of approximately 8.4%. Curve B shows a tenacity of approximately 6.2 ,grams per denier and a percentage elongation at the lbreak of approximately 20.5%.

Curve C represents the Stress-Strain curve of a sample of the same yarn as that of curve A `but to which, for reasons later given, two turns per inch of Z twist had been imparted, and which had been hot stretched 18% at a temperature of approximately 400 F., but without heat setting, reducing its denier to 140. Curve D represents the Stress-Strain curve of a sample of the yarn of curve C which had been subjected to heat shrinkage at 248 F. for a period of one hour at no load. The denier as a result of the shrinkage had increased to 147.

Curve C shows a tenacity of approximately 8.96 grams per denier and a percentage elongation at the break of i approximately 7.0%. Curve D shows a tenacity of approximately 8.3 grams per denier and a percentage elongation at the break of approximately 11.0%.

Referring to FIG. 2 Curve E represents the Stress- Strain curve of a sample of freshly produced Zero Twist 50 Filament Daeron 5100 yarn 220 denier. Curve F represents the Stress-Strain curve of a sample of the same yarn after it had been subjected to heat shrinkage at 248 F. for a periodof one hour at no load.

Curve E shows a tenacity of approximately 6.6 grams per denier and percentage elongation at the break of approximately 9.4%. Curve F shows a tenacity of approximately 5.7 grams per denier and percentage elongation at the break of approximately 20.0%.

Curve G represents the Stress Strain curve of a sample of 50 filament Daeron 5100 yarn, 220 denier, to which two turns of Z twist had been imparted and which had been hot stretched 20% at a temperature of approximately 400 F. but without heat setting, reducing the denier to approximately 189. Curve H represents the Stress-Strain curve of a sample of the yarn of curve G which had been subjected to heat shrinkage at 248 F. for a period of one hour at no load. The denier as a result of the shrinkage had increased to approximately 200.

Curve G shows a tenacity of approximately 8.3 grams per denier and a percentage elongation at the break of approximately 8.0%. Curve H shows a tenacity of approximately 7.9 grams per denier and a percentage elongation at the break of approximately 12.2.

Referring to FIG. 3, Curve K represents the Stress- Strain curve of a sample of Zero Twist 50 Filament Daeron 5500 yarn 250 denier. Curve L represents the Stress-Strain curve of a sample of the same yarn after it had been subjected to heat shrinkage at 248 F. for a period of one hour at no load.

Curve K shows a tenacity of approximately 4.59 grams per denier and a percentage elongation at the break of approximately 14%. Curve L shows a tenacity of approximately 4.13 and a percentage elongation at the break of approximately 27.6%.

Curve M represents the Stress-Strain curve yof the same yarn as that of Curve K but which had been hot stretched 50% at a temperature of approximately 400 F., but without heat setting, reducing its denier to approximately 167. Curve N represents the Stress-Strain curve of a Sample of the yarn of Curve M which had been subjected to heat shrinkage at 248 F. for a period of one hour at no load. The denier as a result of the shrinkage had increased to approximately 174.

Curve M shows a tenacity of approximately 8.43 grams per denier and a percentage elongation at the break of approximately 7%. Curve N shows a tenacity of approximately 8.1 grams per denier and a percentage elongation at the break of approximately 11%.

The stretching of the yarn may be carried out using conventional stretching apparatus.

In commercial practice the hot stretching must be carried out with the yarn moving at relatively high speed for reasons of economical manufacture and to conform the hot stretching step to the speeds at which prior or subsequent conventional operations on the yarn are conventionally carried on, such as twisting, spooling, beaming and the like. It is extremely diicult, if not impossible to directly measure the precise temperature of the resin during the transient heating in a given hot stretching operation. Because of the variables in the heat losses which take place between the heat source and the stretching yarn, the source temperature does not permit a precise calculation of the temperature of the yarn itself but in a given stretching arrangement, the desired yarn temperature in terms of results is easily achieved .by adjusting the source temperature. In the hot stretching of the yarns of FIGS. 1, 2 and 3 the stretching was 4carried out as the yarn passed over a hot plate and the approximate temperature for the yarn of 400 F. given for the yarn during stretching was arrived at by calculations from the temperature of the plate and the theoretical heat losses. To achieve maximum crystallization and best results the stretching temperature should be as close to the melting point of the resin as good manufacturing practice and procedure permits, giving due consideration to product iniformity. Advantageous and useful results for many purposes, however, are lobtained with stretching temperatures as low as approximately 325 F.

The heat stability -of yarns embodying the invention is indicated in the graph of FIG. 4, where the shrinkage vs. time temperature of yarn such as G of FIG. 2 is shown. As is apparent from FIG. 4, after an initial shrinkage of between approximately 4 and 6 percent, for the indicated temperatures the yarn is heat stable and capable of withstanding elastomer curing temperatures without objectionable additional shrinkage over an extended curing period. The initial shrinkage can be minimized in a given coating operation by curing at the lower permissible curing temperatures with a longer curing time.

To take advantage of the physical properties of a yarn such as C and G in the manufacture of rad-omes it is necessary to weave the yarns into a flexible strong fabric and provide such fabric with a permanent coating of a weather resistant, air impervious iiexible material, which, in view of the fact that polyethylene terephthalate is subject to deterioration by ultra-violet light, must also have the property of screening out ultra-violet light. lf the coating is not to add prohibitive weight to the finished fabric the coating material must possess these essential requirements, in sufficient degree to be effective, in relatively thin coatings or the lack supplied by other means.

The polyethylene terephthalate ultra hot stretched yarn of the invention was found diflicult to Weave, due to excessive friction of the shuttle on the warp yarns, and the Weaving operation was attended with a tendency for filament separation and breakage. It was found that the weaveability of the yarn was substantially improved by imparting a few turns, preferably two turns, of Z twist per inch to the yarn prior to its hot stretching, sizing the yarn before weaving with a polyvinyl type size, such as that available from American Analine & Extract Company under the designation 130, and employing monoglyceride antistatic oil as yarn lubricant.

Lightweight fabrics having the desired strength characteristics may be satisfactorily plain woven from this ultra hot-stretched yarn, however, a 2 X 2 basket weave, two picks in the shed, is preferable since it gives a more iiexible fabric and one which more efficiently realizes the advantageous characteristics of the yarn.

The following constructions exemplify those satisfactory for producing a fabric using the ultra hot-stretched yarn of this invention. These constructions provide a minimum weight fabric of maximum strength-weight ratio consistent with all usual conditions of radome and similar uses and, except for a structural instability, objectionable from a manufacturing standpoint and later referred to, meets the requirements of the fabric element in the production of a superior coated radome fabric.

Norm-Fabrics Nos l. 2 and 3 made of yarn C o1' Fig. l. Fabric Nn. 4 made of yarn G of Fig. 2.

The strength characteristics of this ultra hot-stretched polyethylene terephthalate yarn combined with the physical characteristics of the fabric produced therefrom by the weaving procedure and construction above described provides a fabric which, when pre-coated as later described, makes possible the use of chlorosulfonated polyethylene as the weather resistant air impervious coating element of the radome fabric.

Pigmented chlorosulfonated polyethylene has excellent weather resistance, superior resistance to ozone and chemical attack, as well as having excellent color stability. In these respects it far surpasses any of the commercially available coating materials such as neoprene or vinyl chloride heretofore used in constructing radome fabrics. Chlorosulfonated polyethylene, however, because of the incompatability of its Stress-Strain characteristics with those of the previously available fabric structures as Well as its lack of adhesive qualities with respect to fabrics formed from synthetic fibres has not been generally usable for the purpose.

Actinic energy of ultra-violet light has a deleterious effect on practically all transparent polymers. Polyethylene terephthalate is one of the more resistant and chlorosulfonated polyethylene has the property of readily accepting stable inorganic ultra-violet blocking pigments to the extent that excellent resistance to ultra-violet peneration is obtained by coating these fibres to the order of 2 mils. As a result the absorption and screening effect of an extremely thin coating of the pregnated chlorosulfonated polyethylene has been found adequate to protect the Ipolyethylene terephthalate from the ultra-violet light in the suns spectrum.

Having provided an extremely lightweight fabric having the necessary strength for radome use and compatibly conformable to the physical properties of a thin chlorosulfonated polyethylene coating it has been found that the ypreviously mentioned structural instability of the `fabric element can be overcome, and at the same time the insutcient adhesion of the chlorosulfonated polyethylene to polyethylene terephthalate compensated for, by precoating the fabric with a 4% solution of methylene diisocyanate in toluene. The structural instability previously mentioned results from the relative slackness of the basket weave which in -turn results from the small denier of the yarn relative to the end counts. This instability makes it difficult to hold the warp and fill of the 2 x 2 basket weave in uniform position during normal handling and subsequent processing and coating of the fabric.

The yarn may be shrunk at 250 F. prior to Weaving, but preferably, the yarns are Woven into rthe desired fabric construction prior to shrinkage, the woven fabric being passed through a conventional tenter oven of a temperature of 250 F. to impart the desired shrinkage. This has the advantage of a more uniform smoother fabric which is more easily handled in the subsequent coating operations. The shrinkage in this case is taken up under the tension imposed by the tenter, the fabric being shrunk initially slack in the tenter and the loss in tenacity is no greater than that resulting from the preshrinking of the yarn before weaving as previously described and indicated in the graphs in the drawing.

The fabric after shrinkage at 250 F. as previously described is run through a 4% solution of methylene diisocyanate, passing over a bar to remove excess of the solution after which the fabric is festooned to dry the coating. As soon as feasible after this pre-coating, preferably within 24 hours, the fabric is coated on both sides with the chlorosulfonated polyethylene. A suitable chlorosulfonated polyethylene is that commercially available from El. du Pont de Nemours & Co. under the trade name Hypalon The coating is prepared in two parts, A comprising the resin and B comprising the curing system for the resin together with the pigments and other additives. Three representative coating formulas are as follows, parts by weight:

Tri basic lead maleate Benzothiazyl disulphide Tetramethyl-thiuram- 1isulphide Lead acetate Plithalie acid Antimony trioxid Titanium dioxide Phosphate ester type pla Naptlm V M and .P Phthalocyanine Blue Cadmium yellow 3. 6

Cadmium red 1.8

Carbon black l. 9

Total 236. 235. 015 217.33

The Part A may be prepared in a churn by stirring for 4 hours. Part B may be ball milled 18 hours. The Parts A and B should be combined by stirring shortly before use in the following proportions by weight:

TABLE III Coating (1) 100 parts of A with 82.0 parts of B. Coating (2) -100 parts of A with 81.5 parts of B. Coating (3) 100 parts of A with 75.3 parts of B.

The coating may be applied in successive applications with a conventional knife coater to a total Weight of approximately 3 oz. per sq. yd. on one side and approximately 1 oz. per sq. yd. on the other, the fabric being air dried between passes and interlined with a plain nylon or other suitable web between the coating operations. Following the coating the coated fabric is wound on a drum with a Teon impregnated woven glass or other non-adherent interliner and cured in an oven at 250 F. for 1 hour. Alternatively it can be cured continuously in a conventional roto-cure machine.

The comparative unit strength of the fabric of the present invention as represented by the Fabrics Nos. 1 to 4 of Table I after coating with one of the coating materials of Table II compared with that of conventional fabrics now available for radome use are indicated in the following tables:

TABLE IV.-CONVENT1ONAL RADOME FABRICS Pounds breaking strength per inch, per ounce, per square yard Nylon- Fibreglass- R ayon- Rayon- Neoprene Neoprene Neoprene Hypalon Unit Strength 10. 5 12. 28 11.25 10.8

TABLE V.-RADOME FABRIC OF PRESENT INVENTION (Fabrics of Table I-Coatings of Tables II-III) Pounds breaking strength per inch, per ounce, per square yard N0. (l) No. (2) No. (3) N0. (4)

Unit Strength 22. 3 l

Coated fabrics of the described construction have withstood 500 hours of accelerated weathering without loss of strength.

TABLE vL-JOINT CEMENT Part A:

Chlorosulfonated polyethylene Toluene 400 Rosin ester 5 Part B:

Tri basic lead maleate 40 Z-mercapto-imidazoline 1 Diphenylguanidine 2 Antimony trioxide 25 Titanium dioxide 25 Alkyl aryl phosphate type plasticizer 10 Butyl acetate 30 Naphtha 50 The Parts A and B are mixed shortly before use. The so-prepared cement is applied to the parts or edges to be joined and permitted to dry for 10 to 15 minutes. The cemented portions may then be superposed and the joint cured under pressure at a temperature of 250 F. for a period of two hours. Alternatively and preferably the applied cement may be allowed to dry, the joints sealed under momentary pressure, as by a hot iron or roller, and the fabricated structure placed in an oven at curing temperature to cure the joints. Alternatively the material may be butt jointed with overlying strips of the fabric at either side and cured in the same manner. In butt jointing or overlapping, the overlapped or abutting edges are preferably serrated with V cuts, the resulting triangular projections, in the case of butted joints, being intertted in .abutting relation. This arrangement in either case minimizes concentration of stress at the fabric edges under load.

By the use of this cement a joint equal to or exceeding the strength of the fabric may be obtained, even when tested at temperatures of F.

The construction of the present invention provides a heat stable, lightweight radome fabric making possible a radome of less than half the weight without sacrifice of strength.

An unprecedented adhesion of the chlorosulfonated polyethylene to the polyethylene terephthalate is obtained.

Heat stable yarn with a strength-weight ratio 50% greater than previously available polyethylene terephthalate yarns have been produced commercially using the hot-stretching techniques above disclosed. The yarn 'retains a tenacity of over 8 grams per denier after heat shrinkage. In coated fabrics where a low temperature curing system is permissible or available, greater fabric strengths are possible.

While the super hot-stretched yarn of the invention has a special utility in the radome fabric above described, it nds use in any fabric or structure where high tenaciy is of advantage and in uses where high temperatures, such as coating curing tempenatures are not involved, tenacities in excess of 9 grams per denier are made available.

When converted into engineering terms, this tenacity rep-` resents a tensile strength of approximately 163,000 pounds per square inch. Such a material has many possible structural uses such as a reinforcing material for laminated plastics. Furthermore, a polyethylene terephthalate yarn of exceptionally low elongation is provided. The yarn of the invention is further characterized by the absence of substantial yielding at low stress levels as indicated in curves C and E of the gure.

What is claimed is:

1. A woven and coated fabric comprising .a fabric formed of mu-ltilament polyethylene tereph-thalate yarns and provided on each side with an undercoat of methylene diisocyanate yand a curved overcoat of chlorosulfonated polyethylene.

2. A woven and coated fabric comprising a fabric formed of multilament polyethylene terephthalate yarns and provided on each side with an undercoat of methylene diisocyanate and -an overcoat of cured chlorosulfonated polyethylene, the yarn being form `stable at .a temperature inthe curing range of chlorosulfonated polyethylene.

3. A woven and coated fabric comprising a fabric formed yof multilament polyethylene terephthalate yarns and provided on each side with an undercoat of methylene diisocyanate 'and an 'overcoat of cured chlorosulfonated polyethylene, the yarn being form stable at a temperature in the curing range of chlorosulfon-ated polyethylene, and having a tenacity of at 'least 7 grams per denier, and an ultimate elongation of not over 11%.

4. A Woven and coated fabric comprising a fabric formed of multifilament polyethylene terephthalate yarns hot stretched at a temperature labove 390 F. substantially to the point of ultimate molecular orientation, -the fabric being shrunk at a temperature in the curing range of chlorosulfonated polyethylene, said fabric being provided on each side ywith yan undercoat of methylene diisocyanate and an overcoat of cured chlorosulfonated polyethylene.

5. A woven .and coated fabric comprising a fabric formed of multilament polyethylene terephthalate yarns having a tenacity of at least 7 grams per denier, an untimate elongation of not over 11% and form stable at a temperature within the curing range of chlorosulfonated polyethylene, said fabric being coated on each side with an undercoat of methylene diisocyanate and an overcoat of cured -chlorosulfonated polyethylene.

6. A Woven and coated fabric as in claim 5, the total Weight of the coatings on one side approximating 3 ounces per square yard and the Weight of the coatings on the other side approximating 1 ounce per square yard.

7. A woven and coated fabric .as in claim 5, the chlorosulfonated polyethylene being pigmented to screen the yarn from ultraviolet light.

8. A woven and coated fabric as in claim 7 the pigmented chlorosulfonate-d polyethylene coatings being approximately 2 mils in thickness.

References Cited UNITED STATES PATENTS 2,556,295 6/1951 'Pace 18--54 2,556,885 6/1951 Ness 117-76 2,723,935 11/1955 Rodman 161-190 X 2,826,526 3/ 1958 Meyrick et al.

2,854,425 9/1958 Boger et al.

2,919,206 12/ 1959 Myalmquist 117-76 2,93 8,823 5/1960 Salem et al.

3,037,261 6/1962 Hess 28-74 3,060,549 10/ 1962 Horton 28-74 ALEXANDER WYMAN, Primary Examiner. R. C. MADER, Examiner. W. A. POWELL, H. G. GARNER, Assistant Examiners. 

1. A WOVEN AND COATED FABRIC COMPRISING A FABRIC FORMED OF MULTIFILAMENT POLYETHYLENE TEREPHTHALATE YARNS AND PROVIDED ON EACH SIDE WITH AN UNDERCOAT OF METHYLENE DIISOCYANATE AND A CURVED OVERCOAT OF CHLOROSULFONATED POLYETHYLENE. 